An IARC Monographs Working Group has concluded that indoor emissions from household combustion of coal are carcinogenic to humans (Group 11), after a thorough review of the published scientific evidence.At the same time, the Working Group concluded that indoor emissions from household combustion of biomass fuel2 (mostly wood) are probably carcinogenic to humans (Group 2A1).To complement these evaluations of indoor air pollutants, the Working Group also assessed the potential carcinogenicity of emissions from high-temperature frying.These emissions were also evaluated as probably carcinogenic to humans (Group 2A1).A summary of the IARC evaluation is published in the Policy Watch section of the December issue of The Lancet Oncology, and the results will be presented at the Society for Risk analysis Annual Meeting in Baltimore (USA) on December 4.

Risk reduction measures

Exposure to polluted indoor air from combustion of wood or coal or from frying can be greatly reduced by adequate ventilation, e.g. through the construction of a chimney, as has been shown in China. This seems an obvious first public health measure to start reducing the lung cancer burden for large parts of the world's population. Changing cooking and heating methods should also be considered.The Working Group, comprising 19 scientists from 8 countries, was convened by the IARC Monographs Programme of the International Agency for Research on Cancer (IARC), the cancer research agency of the World Health Organization.

Major public health importance"This new IARC Monograph (volume 95) addresses exposures that are experienced daily by hundreds of millions world-wide," said Dr Peter Boyle, Director of IARC. It is estimated that approximately half the worlds population uses wood or coal for cooking and heating, often in poorly ventilated, and often unventilated, spaces. For instance, in Sub-Saharan Africa, the percentage of households using solid fuels climbs to over 90%. "It is therefore of enormous public health importance that we call attention to the health risks of what is daily practice for so many people", he continued.

Coal risks not newOccupational exposure to coal combustion products has long been known to cause lung cancer. Products of incomplete combustion contain respirable particles and many organic chemicals, including known human carcinogens such as benzo[a]pyrene, formaldehyde and benzene. Average indoor concentrations of fine particles (< 10 micrometres) can be as high as several milligrams per cubic metre, with peak concentrations ten times higher. On the basis of conclusive epidemiological evidence, the Working Group evaluated indoor emissions from household combustion of coal as carcinogenic to humans (Group 11). Dr Boyle stressed that There are parts of the world where women and young children especially are exposed to these high levels of indoor air pollution for most of their day. Fortunately, these exposure levels can be greatly lowered, and the cancer risk reduced.

Wood smoke a probable carcinogen While the association of emissions from coal combustion with lung cancer was relatively clear-cut, the evidence of increased cancer risk associated with emissions from biomass combustion (mainly from wood) was less studied : these emissions were classified as probably carcinogenic to humans (Group 2A1).

and so is high-temperature fryingTo complete this review of indoor air pollution, the Working Group evaluated the potential carcinogenicity of various ways of frying: stir-frying, deep-frying and panfrying, which involve heating oil to high temperatures, are practiced worldwide and are particularly widespread in East Asia. On the basis of limited data in humans and conclusive evidence in experimental animals, the Working Group concluded that emissions from high-temperature frying are probably carcinogenic to humans (Group 2A1). This classification was supported by a wealth of experimental data on the mutagenicity of emissions of cooking oil at temperatures around 230 degrees Celsius. The frying method or type of oil used did not seem to have a big influence on the results of the epidemiological studies.

Evaluating carcinogenic risks to humansThe IARC Monographs Programme on the evaluation of carcinogenic risks to humans has traditionally focused its attention on the evaluation of occupational and lifestyle exposures in populations of the developed, industrialized world. This new monograph deals with an exposure that is widespread in low- and medium-resource countries, and reflects how the Monographs Programme has broadened its scope and reach.

1 See the definitions in the Appendix below2 Biomass includes wood, charcoal, dung and unprocessed vegetal residue.